Illumination devices based on semiconductor light sources, such as light-emitting diodes (LEDs), offer a viable alternative to traditional fluorescent, HID, and incandescent lamps. Functional advantages and benefits of LEDs include high energy conversion and optical efficiency, longer expected lifetime, lower operating costs, and many others.
In some applications, an LED-based lighting unit may include a lighting driver which supplies an LED driving current to a plurality of LED modules, each including one or more LEDs. For example, an LED module may include a circuit board (e.g., a printed circuit board) having one or more LEDs mounted thereon. Such circuit boards may be plugged into slots in a lighting fixture, or a motherboard, on which the lighting driver may be provided.
In various applications and installations, an LED-based lighting unit may include different numbers of LEDs and/or LED modules. For example, the number of LEDs and LED modules may be changed depending on the light output requirements, e.g. lumens, for a particular installation.
From a manufacturing standpoint, it would be desirable for a manufacturer to reduce the number of different components that they need to manufacture and maintain in stock to assemble a large number of different LED-based lighting units having a wide variety of light output requirements. Accordingly, it would be desirable to be able to use the same lighting driver for different LED-based lighting units which have a wide variation in the number of LEDs and LED modules which are included therein.
In general, the magnitude or level of the LED driving current output by a lighting driver will need to be changed according to the number of LEDs and LED modules to which it is connected and which it drives. This means that if a single lighting driver is going to be employed in a variety of LED-based lighting units with different numbers of LEDs and/or LED modules, then the lighting driver will have to include a means or provision for adjusting the LED driving current to match the current driving requirements for the different LED lighting units according to the different numbers of light sources that they include. Meanwhile, the number of LEDs and LED modules to be included in a particular LED-based lighting unit is determined at the time of manufacturing that LED lighting unit. Thus, if the same lighting driver is to be employed in a variety of LED lighting units with different numbers of LEDs and LED modules, then the lighting driver would have to be programmed at the time of manufacturing for each different LED lighting unit so that its output LED driving current is appropriate for the particular number of LEDs and LED modules that are included in that LED lighting unit.
However, individually programming the lighting driver of each LED-based lighting unit imposes costs and constraints on the manufacturing environment. For example, such programming may require that the manufacturing facility include special equipment and personnel with special knowledge and ability to program the lighting driver at the time when the number of LED modules is selected for the LED lighting unit.
On the other hand, as noted above, if a lighting driver with a fixed LED driving current is used for each LED-based lighting unit that has a different number of LED modules, then the manufacturing facility will be required to build and stock a large number of different lighting drivers. Furthermore, field repair or replacement of lighting drivers becomes more complicated and expensive if there are a large number of different lighting drivers, each corresponding to a particular LED lighting unit having a particular number of LEDs and LED modules.
Another issue that arises with LED-based lighting units pertains to temperature. The lifetime of an LED is substantially affected by the temperature at which it is operated, which in turn is affected by the LED driving current flowing through it. So it would be desirable for a lighting driver to be able to reduce the current passing through an LED when its temperature increases above a nominal temperature, or a threshold temperature, so as to decrease the temperature of the LED and thereby extend its lifetime.
Thus, it would be desirable to provide a lighting driver, and an LED-based lighting unit that includes a lighting driver which can satisfy one or more of these needs.